Significant advances have been made in the technology of white light-emitting diodes. White light-emitting diodes are commercially available which generate 60˜100 lumens/watt. This is comparable to the performance of fluorescent lamps; therefore there have been a lot of applications in the field of lighting using white light-emitting diodes.
Various light-emitting diode driver circuits are known from the prior arts. For example, U.S. Pat. No. 6,304,464: “FLYBACK AS LED DRIVER”; U.S. Pat. No. 6,577,512: “POWER SUPPLY FOR LEDS”; and U.S. Pat. No. 6,747,420: “DRIVER CIRCUIT FOR LIGHT-EMITTING DIODES”. All the light-emitting diode driver circuits mentioned above are constant current regulator circuits that act as constant current sources to drive light-emitting diodes.
In the field of lighting applications, for a white light-emitting diode lamp driven by a constant current source and a fluorescent lamp driven by an alternating current source under the condition that both lamps' remitted illumination have the same average illumination value, the fluorescent lamp provides higher perceived brightness levels than the white light-emitting diode lamp, the main reason is: human eyes are responsive to the peak value of illumination; therefore, if a lamp can provide higher peak illumination, it provides higher perceived brightness levels. For a fluorescent lamp driven by an alternating current (AC) source, it remits illumination with peak value higher than its average illumination value. But for a white light-emitting diode lamp driven by a constant current source, since light generation of a white light-emitting diode is dependent on the current strength through the white light-emitting diode, it remits illumination with peak value close to its average illumination value. Therefore, a white light-emitting diode lamp driven by a constant current regulator circuit constitutes a drawback of its remitted illumination with low perceived brightness levels.
It would be desirable to have a light-emitting diode driving circuit that would overcome the above disadvantages.